1. Field of the Invention
The invention relates to novel bleach precursors, detergent compositions containing these precursors and methods for removing stains using these compositions.
2. Related Art
It is well-known that active oxygen-releasing compounds are effective bleaching agents. These compounds are frequently incorporated into detergent compositions for stain and soil removal. Unlike the traditional sodium hypochlorite bleaches, oxygen-releasing compounds are less aggressive and thus more compatible with detergent formulations. There is, however, an important limitation to these bleaches; activity is extremely temperature dependent. Thus, oxygen-releasing bleaches are essentially only practical when the bleaching solution is heated above 60.degree. C.. At a temperature of just 60.degree. C., extremely high amounts of the active oxygen-releasing compounds must be added to the system to achieve any bleach effect. Although this would indicate the desirability of high temperature operation, high temperatures are both economically and practically disadvantageous.
At bleach solution temperatures below 60.degree. C., the active oxygen-releasing compounds are rendered much less effective regardless of their level in the system. With respect to bleaching of laundry in automatic household washing machines, it must be noted that these machines are normally operated at wash-water temperatures below 60.degree. C. Consequently, there has developed a need for substances which promote release of active oxygen at temperatures below 60.degree. C. These substances are generally referred to in the art as bleach precursors, although they have also been called promotors and activators. Normally, bleach precursors are used in conjunction with persalts capable of releasing hydrogen peroxide in aqueous solution, perborate being the most widely used persalt.
Typically, the precursor is a reactive compound such as a carboxylic acid ester that in alkaline detergent solution containing a source of hydrogen peroxide, e.g. a persalt, will generate the corresponding peroxy acid derivative. The reaction involves nucleophilic substitution onto the precursor by hydroperoxyl anions (HOO--) and is facilitated by precursors having good leaving groups. Often the reaction is referred to as a perhydrolysis.
Early patents in the area of precursor chemistry include U.S. Pat. No. 3,256,198 (Matzner) and U.S. Pat. No. 3,272,750 (Chase) each of which suggest the use of organic carbonate esters as bleach aids. Unfortunately, some of the better bleaching esters were later found to have a malodor problem.
British Patent 836,988 (Davies et. al.) and British Patent 864,798 (Hampson et. al.) were forerunners disclosing the use of aliphatic carboxylic acid esters as adjuncts for accelerating the bleaching of persalts such as sodium perborate or percarbonate.
U.S. Pat. No. 4,283,301 (Diehl) discloses a peroxygen bleach and a precursor of the general formula: ##STR2## wherein R is an alkyl chain containing from 5 to 13 carbon atoms, R.sup.2 is an alkyl chain containing from 4 to 24 carbon atoms and each Z is a leaving group as defined therein.
U.S. Pat. No. 4,412,934 (Chung et. al.) reports compositions incorporating bleach precursors of the general formula: ##STR3## wherein R is an alkyl group containing from 5 to 18 carbon atoms and L is a leaving group.
Similar disclosures are found in U.S. Pat. No. 4,486,327 (Murphy et. al.), EP 0 098 129 (Hardy et. al.), EP 0 106 584 (Hartman), EP 0 106 634 (Chung et. al.), EP 0 120 591 (Hardy et. al.), EP 0 163 331 (Burns et. al.), EP 0 166 571 (Hardy et. al.), EP 0 185 522 (Fong et. al.), EP 0 170 386 (Burns et. al.), EP 0 153 222 (Moyne et. al.), EP 0 153 223 (Moyne et. al.) and EP 0 202 698 (Nollet et. al.). Among the preferred leaving groups are those having solubilizing functionality including sulfonic, sulfuric, carboxylate and quaternary ammonium salt groups.
A typical precursor within the concept of the aforedescribed patents is sodium n-nonanoyloxybenzene sulfonate presently commercialized as a component of a branded detergent. This sulfonate, in combination with sodium perborate, effectively releases peroxygen fragments upon perhydrolysis, as well as sodium 4-sulfophenolate. For environmental and other reasons it may be desirable to avoid the use of sulfophenol salts.
While the aforementioned precursors have all been reported effective at stain removal, there is still a need for more efficient systems. Stain removal efficiency may be improved either by a precursor that generates equivalent bleach at a lower precursor molar level or operates at lower levels of hydrogen peroxide source. Not only do lower levels of peroxide source or precursor provide better economics, they also permit increased flexibility in detergent formulation.
Consequently, it is an object of the present invention to provide a detergent-bleach composition with a precursor that permits bleaching over a wide temperature range including that of under 60.degree. C.
Another object of the present invention is to provide certain novel bleach precursors which have hitherto not been described in the art.
A further object of the present invention is to provide bleach precursors which are of pleasant odor.
A still further object of the present invention is to provide a precursor that can be economically synthesized from readily available starting materials and in a minimum number of synthetic steps.
These and other objects of the present invention will become more readily apparent by consideration of the detailed description which follows.